Use of power take offs (PTOs) to transmit engine power to a driven component, such as wood chipper or other industrial applications, are well known in the art. Manufacturers of existing systems include Rockford Powertrains of Rockford, Ill., Twin Disc of Racine, Wis., Funk Manufacturing of Coffeyville, Kans., and Stein Manufacturing. All of the PTOs produced by these manufacturers consist of a mechanical clutch that transfers the power of the engine through an output shaft by engaging a lever that is independent of engine controls.
A number of problems result from this approach. One problem is that in many cases, the operator increases engine speed (increased revolutions per minute or RPM) during engagement of the clutch so that the driven device may be driven by the engine without stalling the engine. Such high RPM engagement of existing mechanical clutches often damages, and in some cases destroys, the clutch and other components, including engine components and driven components.
Another problem with the PTOs of the prior art arises with regard to known methods for lubrication. Currently manufactured PTOs either provide too little or too much lubrication. Too little lubrication causes parts to wear and eventually seize, resulting in unit failure. On the other hand, too much lubrication causes slippage and eventual failure. Specifically, many of the industrial transmissions of the prior art include, for example, couplings and other parts that require periodic service lubrication. Lubrication for these parts, as well as protection from external elements, is typically provided through use of grease fittings attached to rubber hoses or other covers for the parts. In addition to causing failure of the lubricated parts, failure of these fittings or covers can also result in grease from the fittings interfering with the operation of other parts of the transmission, such as clutch plates. Such interference can also result from incorrect replenishing or spillage of grease when added to the fittings. Further, manufacturers may not provide clear or sufficient maintenance instructions for lubrication, or the lubrication needs may vary widely from standard recommended lubrication because of severe loads or uses of the driven device.
Another problem with the PTOs of the prior art is that these devices typically are limited to transmitting the same amount of power that the engine delivers. Thus, for example, if the load demand of the driven component exceeds the output power of the engine, a complete and sudden shutdown of the engine will occur, and in some cases, catastrophic damage can result. Another typical result of this event is excessive machine downtime.
Further, while it is known in the art to use torque converters in industrial applications, their use is often problematic. Torque converters, such as those produced by Transfluid Industrial Transmissions of Milano, Italy, can be difficult to use in many applications because their engagement and disengagement is controlled by fluid pressure, rather than a positive or direct engagement by an operator. The engagement of these torque converters at particular fluid pressures results from a combination of RPM of the driving engine and other factors that often cannot be controlled by the operator. For example, one such factor is the viscosity of the fluid medium, which can vary widely depending on temperature. Thus, it is often difficult for an operator to accurately control the engagement and disengagement of torque converters used in industrial applications.
Another problem with existing fluid-driven transmissions is high fluid pressure, which can result in stall conditions in applications lacking a positive neutral or positive engagement/disengagement feature. For example, some prior art fluid-driven transmissions include lead plugs within the drive housing. These plugs are released if excessive fluid pressure buildup occurs, such as in the event of stall. When the plugs are released, the fluid leaks out of the plug openings and creates a maintenance and potentially an environmental hazard.
Accordingly, there is a need for a variably engageable transmission for industrial applications. There is a further need for an industrial transmission that may not be engaged at speeds other than idle. There is a further need for an industrial transmission that is self-contained, self-lubricating, and self-cleaning to maximize performance and minimize part wear. Finally, there is a need for a transmission having the capability to multiply the torque capabilities of the driving engine.
Specifically, there is a need to provide a variable engageable transmission for industrial and other applications that incorporates use of a fluidly engageable clutch assembly and a torque converter. There is an additional need to provide a variably engageable transmission that overcomes the two major problems with use of a fluid coupling, which include lack of a positive neutral and the tendency of fluid couplings to overheat upon load stalls of more than 30 seconds. There is also a need for an industrial transmission that provides for direct application of power from the engine to the driven device, without complicating gears, and that is engageable simply through a combination throttle and clutch engagement feature.